1. Field of the Invention
The present invention relates to a plasma processing apparatus. More particularly, the present invention relates to a plasma processing apparatus which uses materials which are either a liquid or a solid at normal temperature and normal pressure as gaseous raw materials and which is suited to form uniform, high-quality films on substrates having a large area, and to a method of processing substrates by using the apparatus.
2. Description of the Related Art
In a conventional plasma processing apparatus, treatment gas is introduced to a vacuum container through an introduction tube, and treatment gas is blown off perpendicularly to the surface of a substrate within the vacuum container in order to uniformly process a large area of the substrate, as disclosed in Japanese Patent Laid-Open No. 1-287926.
As also disclosed in Japanese Patent Laid-Open No. 1-236635, what is commonly called a microwave plasma apparatus using electron cyclotron resonance (ECR) to process high-quality thin films of oxidized film types over a large area thereof is known.
In the former plasma processing apparatus of the above-described prior art, ozone is used as a plasma seed. However, as highly excited oxygen ions are indispensable for the formation of high-quality oxidized films, there is a problem in that high-quality oxidized films cannot be formed by an apparatus using ozone as described above.
No problem arises when a gaseous raw material which is a gas at normal temperature and normal pressure is used in the latter plasma processing apparatus. However, when a gaseous raw material in which what is commonly called an aggregate (a liquid or solid at normal temperature and normal pressure) is gasified, is used, since the gaseous raw material is adiabatically expanded at the opening portion of the introduction tube and the temperature near the opening portion decreases considerably, the gaseous raw material liquefies or solidifies and is deposited on the opening portion of the introduction tube, causing the opening portion to be clogged.
Since the leading edge portion of the introduction tube projects into the vacuum container, heating may be insufficient depending upon the degree of cooling during adiabatic expansion. Therefore, the opening portion may be clogged, and the propagation efficiency of microwaves becomes poor. The substrate is not uniformly processed, decreasing processing efficiency.